Greenhouse Exhaust Fan An exhaust fan can be an important component of a greenhouse to help regulate temperature, humidity, and air quality. Here are some factors to consider when selecting an exhaust fan for a greenhouse: Size: The size of the fan needed will depend on the size of your greenhouse. A good rule of thumb is to have a fan that can move at least one cubic foot of air per minute (CFM) for every square foot of greenhouse floor area. For example, a greenhouse with 100 square feet of floor area would need a fan with a minimum capacity of 100 CFM. Ventilation needs: Determine how often you want the air in your greenhouse to be completely exchanged. This is called the air exchange rate and is measured in air changes per hour (ACH). A good starting point is to aim for at least four ACH in the summer and two ACH in the winter. Power source: Consider whether you want an electric or solar-powered exhaust fan. An electric fan can provide greater capacity and control, but a solar-powered fan can be more cost-effective and environmentally friendly. Noise level: Greenhouses are often used for relaxation and meditation, so you may want to consider a fan with a low noise level.